1. Field of the Invention
The present invention relates to a rotation angle detection device equipped with a non-contact sensor that detects a rotation angle of a rotary member by detecting a change in the direction of a magnetic flux.
2. Description of the Related Art
In a known conventional rotation angle detection device for detecting a rotation angle of a throttle valve, an angle sensor is surrounded by a segment type permanent magnet, and the outer periphery of a pair of opposing permanent magnets is surrounded by a ring-shaped yoke (see, for example, JP 2004-332632 A (FIGS. 5 through 9).
In this conventional rotation angle sensor, by controlling the segment center angle of the permanent magnet to a predetermined value, it is possible to obtain, between the opposing permanent magnets, magnetic fields whose magnetic lines of force generated are parallel to each other. As a result, the influence of any positional deviation between the permanent magnet and the angle sensor on the output signal of the angle sensor is suppressed to a minimum.
In the above-described rotation angle detection device, however, the peripheral length of the permanent magnet is rather large, which leads to a large permanent magnet size, resulting in an increase in cost. Further, to attain high machining accuracy for the permanent magnet, the number of machining processes has to be increased.